1. Field of the Invention
The present invention relates to a falling film evaporator which is arranged to effect heat exchange by utilizing the evaporation of a liquid film during downward flow thereof and, more particularly, to a falling film evaporator of the type suitable for use in various kinds of system for effecting cooling of equipment, an apparatus for supplying cooling water for air-conditioning and an electric power plant using ocean thermal energy.
2. Description of the Related Art
A conventional type of falling film evaporator described in, for example, Japanese Patent Unexamined Publication No. 59-212601 and U.S. Pat. No. 4,520,866. This kind of evaporator has the following structure. Liquid refrigerant flows into an evaporator shell through a liquid refrigerant inlet formed in an upper portion of the evaporator shell, and flows down in the form of a thin film over the outer surfaces of a multiplicity of heat exchanger tubes provided within the evaporator shell. The liquid refrigerant evaporates by absorbing the heat of the cooling water flowing in the heat exchanger tubes, and thus cools the cooling water. The resultant gasified refrigerant flows out through a refrigerant gas outlet. The cooling water thus cooled flows out of the evaporator through a cooling water outlet, then enters the line of an object to be cooled, and is subsequently returned to the cooling water inlet of the evaporator by the circulating motion of a circulating pump.
In a refrigeration cycle which incorporates the above-described conventional falling film evaporator, the refrigerant which has been nearly gasified by the evaporator is supplied to a compressor, but if an excessive amount of liquid refrigerant is supplied to the compressor, it may be damaged. For this reason, a gas-liquid separator is provided between the evaporator and the compressor in order to reserve the extra portion of the liquid refrigerant which has been left in a liquid state because of its imperfect evaporation in the evaporator which often takes place during system start-up or due to a decrease in the temperature of a heat load. In addition, the gas-liquid separator is adapted to recover a portion of the compressor-lubricating oil stored in a bottom portion of the evaporator, through a pipeline which is disposed separately from a refrigerant gas outlet pipeline. However, the gas-liquid separator which is disposed between the evaporator and the compressor in the above-described manner has the problems of increasing the overall size of the apparatus and of producing pressure loss and heat loss to deteriorate the efficiency of the refrigeration cycle.